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Why Is the Mortality Rate from Acute MI Higher in December?

Am Fam Physician. 2006 Apr 15;73(8):1454-1456.

Patients hospitalized for acute myocardial infarction (MI) in December have higher mortality rates than at any other time of year, regardless of climate or geographic region. Because evidence-based therapies are known to improve clinical outcomes following acute MI, it is possible that increased mortality in December may result from less frequent use of these therapies compared with other months. To test this hypothesis, Meine and colleagues conducted a retrospective analysis of data from the Cooperative Cardiovascular Project, a large quality-improvement study of Medicare beneficiaries with confirmed acute MI.

The study population consisted of 127,959 patients 65 years or older who were admitted to nonfederal, acute care hospitals with a primary diagnosis of acute MI between January 1994 and February 1996. Acute MI was defined as a greater than 5 percent elevation in creatine kinase–MB level or onset of chest pain within the previous 48 hours associated with characteristic electrocardiographic changes. In addition to 30-day mortality rates, information was obtained on admission regarding the use of aspirin and beta blockers, smoking cessation counseling, and coronary reperfusion (i.e., history of thrombolytic therapy or percutaneous coronary intervention). A subset of 14,492 patients who were admitted during December was compared with the rest of the study population. Statistical models were used to control for potential confounding variables such as demographic characteristics, socioeconomic status, physician and hospital characteristics, and the presence of contraindications to each of the evidence-based therapies.

Confirming findings from previous studies, the authors found that the 30-day mortality rate for patients admitted with acute MI in December was significantly higher than for patients hospitalized during the rest of the year (21.7 versus 20.1 percent, P < .001). After adjusting for confounding variables, they found no statistically significant difference between the two groups in the provision of the evidence-based therapies.

The authors conclude that the observational data do not support the hypothesis that higher mortality rates from acute MI in December are related to less frequent use of evidence-based therapies. They assert that further research is needed to clarify a viable mechanism for the occurrence of higher mortality rates.

editor’s note: Although this study’s focus was a comparison of evidence-based therapies for acute MI between two groups of patients, the statistic that stands out is the number of patients overall who should have received one or all of these therapies but did not. The percentages of patients who were prescribed aspirin (69 percent), beta blockers (30 percent), and smoking cessation counseling (6 percent) at hospital discharge were disappointingly low. Although the past decade has witnessed impressive progress in the high technology of percutaneous coronary interventions following an acute MI, improved long-term clinical outcomes remain inextricably linked to the prescription of these “low-tech” therapies with angiotensin-converting enzyme inhibitors and statins.1 It is the duty of family physicians to make sure that patients with a history of acute MI have access to these proven therapies.—k.w.l.